The present invention relates to a method and apparatus for saving energy when joining a connecting piece of metal with a metal surface by pin brazing, wherein heat is generated by an electronic welding arc and the required energy for the process is carefully supervised and controlled and wherein structural changes such as martensite formations, are minimized under the brazing site in, for example, a railway track or in pipe lines.
A conventional method for producing the above mentioned connections is described in Swedish patent 129 849 and 8404050-0.
One problem with using the conventional methods on railway tracks is that the strong heat released under the brazing site causes a proportionately strong martensite formation, which, in turn, can result in crack formations.
A further problem is the large energy consumption of the conventional methods, among other things, due to the use of brazing pins having a timed wire (or fuse wire). This wire, which is usually made of copper, regulates the duration of the welding process by melting after a certain period of time. This, in turn, causes the current supply to cease. Furthermore, the conventional equipment includes many contacts with large energy consumption. All these items result in fewer brazings for each current supply unit.
Another problem with the conventional methods involves the fact that at the beginning of the process, the brazing pin is raised up from the work-piece a distance of about 2 mm. This distance must be manually adjusted with precision and must be controlled visually, in an arrangement in a brazing gun, at every brazing occasion in order to avoid brazing failure and high martensite formations.
A still further problem with conventional pin brazing methods is that the current from the current sources normally used, is not constant. The current usually comes from a source consisting of batteries. The current used when brazing is not constant, and varies usually depending on the battery, cables, fuse wire, contact passages in the brazing gun as well as the length of the welding arc. These variables result in unsatisfactory brazing and large structural changes in the work material. Furthermore, the distance between the brazing pin of the brazing gun and the work piece increases as the brazing pin melts down, which, in turn, affects the current.
Another problem with conventional methods is that the work-piece can be insufficiently grounded thus resulting in a failed brazing and consumption of material.